Competitive adsorption of heavy metals by soils of Aligarh district.

This study was conducted to evaluate the selectivity sequence and to estimate the competitiv e adsorption of several heavy metals (Pb, Cr, Cu, Zn, Cd and Ni) on ten different soils of Aligarh district. The results indicated that the Langmuir isotherm could well describe the adsorption of all these heavy metals on all the studied soils. Results indicated that all the soils have a maximum sorption capacity and binding strength for Pb. Metal solid/liquid distribution coefficients (Kd), which represent the adsorption affinity of the metallic cations in solution for the solid phase were also calculated. On the basis of Kd values, the most common sequence of preference was Pb > Cr > Cu > Cd > Zn > Ni,, which may be correlated with their first hydrolysis equilibrium constant. The adsorption of heavy metals was significantly positively correlated with soil organic matter and soil CEC while negatively correlated with soil pH. The values of Langmuir constants and Kd also suggest that the adsorption was in the order of soil samples as S1 > S 2 > S 3 > S 10 > S 4 > S 5 > S 6 > S 7 > S 8 > S 9.